Overhead doors or curtains are commonly counterbalanced by torsion spring assemblies, such an assembly generally including a support shaft which extends through the spring and is not only anchored to one end of the spring but is also adjustably fixed to a frame that in turn is mounted upon the building structure. The opposite end of the spring is connected to a tubular barrel that covers the spring and provides the means for supporting the hinged panel door or curtain. Selected tension is imparted to the spring and is transmitted by the barrel to counterbalance or compensate for the weight of the door.
It is also well known that replacement of such a spring in the field can be difficult and, in some cases, even dangerous. The difficulty frequently centers on the steps of properly forming the ends of such a spring and then securely connecting them to the anchoring sleeves while simultaneously stretching the spring to space its coils apart, thereby allowing space for additional coils to be formed later as the spring is twisted to perform its counterbalancing function. (Typically, such a spring is wound with no gaps or spaces between its coils when the spring is a free or untensioned state.) The "forming" operation commonly includes heating each end of the spring with a torch or other suitable means to a cherry red condition so that the wire can be bent or securely connected to each anchoring collar. Such an operation requires substantial time and special equipment during manfacture and is especially difficult to carry out in the field when a broken spring is to be replaced. Also, depending on the amount of heat applied to the wire during bending, the physical properties of the spring material may be adversely affected, increasing the risks of premature spring breakage.
Unlike a conventional counterbalance spring, the torsion spring of this invention is formed with spaces between its coils and is compressed rather than stretched during assembly with the other parts. The spring includes pre-formed radially-extending hook portions at its opposite ends which are received in slots provided in reduced neck portions of the spring-mounting collars. During assembly, the spring is fitted onto a shaft which has one of the collars already mounted at its distal end, the hook at the distal end of the spring is inserted into the slot of the collar, the spring is then compressed, and the second collar is mounted upon the shaft at a distance from the first collar only slightly less than the length of the spring in an untensioned state. The compressive forces applied to the spring are then released and the hook portion at the spring's proximal end is inserted into the slot of the second anchoring collar.
Such a construction allows the torsion spring assembly to be quickly, easily, and safely assembled in the field or during manufacture. Of particular importance during field assembly is the fact that no specially-designed tools are required for spring replacement and no on-site heating and forming steps are performed. These and other important advantages, features, and objects of the invention will become apparent from the following specification and drawings.